The invention relates to the control of the base of a power transistor used in high tension switching.
In choppers and chopped power supplies of a relatively low power, for example between 30 W and 500 W, a power transistor is generally used whose collector-emitter Vce bias is formed by the rectified AC mains and to the base of which are applied current pulses, of a frequency between 20 and 100 KHz for example. This transistor operates under saturated ON condition during the interval of a pulse, and under off condition in the intervals between one pulse and the next pulse.
To increase the switching frequency, while minimizing the losses and, when the circuit comprises a regulation loop, so as to obtain satisfactory regulation dynamics, it is important to minimize the saturation storage time of the transistor, which is often achieved by providing the base control device with a so-called "anti-saturation" diode circuit, which ensures that the transistor will not become saturated in the ON condition.